Method for producing a bung for a metal cask

ABSTRACT

A method for producing a bung for a metal cask that does not require a conventional collar and seal, and that simplifies the operations for forming the bung. The method disclosed in the present application includes the following steps. First, a prestamping operation creates a preforming dome in the wall of the cask such that a cuvett is formed. Second, an approximately cylindrical shaft is formed by stamping and thus puncturing the wall of the cask at the location of the bung. Third, the protruding edge of the shaft is folded down the to form an external rolled edge. Fourth, encircling the shaft with a rigid ring constituted by at least two annular sections such that the metal does not tear during the formation of the threads. Finally, the method of the present invention includes the step of implementing a roller threading head to form internal threads in the shaft.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] French patent application 00/00638, filed Jan. 19, 2000 PCT application WO 01/53021 A2, filed Jan. 18, 2001

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method for producing a bung for a metal cask, in particular producing a bung for a relatively thin-walled cask, typically less than 2 mm thick. It relates to an improvement making it possible to simplify the production of such a bung and to reduce the cost price.

[0004] 2. Description of the Related Art

[0005] A well known method for producing a bung for a metal cask, in particular a thin-walled cask, includes slipping onto the wall of the cask a collar which is prefabricated, relatively thick and internally threaded. Such a collar has a flat octagonally-shaped base. The wall of the cask is pierced and the metal is shaped around the piercing by making both an octagonal impression on the internal side and a cylindrical shaft extending outwards. The collar is inserted in the shaft in such a way that its octagonal base fits into the corresponding impression, with the insertion of a seal. The fixing of the collar is ensured by its rolled edge on the rim of the shaft.

BRIEF SUMMARY OF THE INVENTION

[0006] The present invention makes it possible to purely and simply do away with the collar and the seal while simplifying the operations for forming the bung. To this end, the invention relates to a process or method for producing a bung for a metal cask. The method includes forming an approximately cylindrical shaft by stamping the wall of the cask, and forming a thread inside this shaft.

[0007] For thin sheet metal, roller form threading is used making it possible to obtain the thread without removing any metal. It should be noted that this type of roller form threading is not usually possible on thin sheet metal. Advantageously, however, the shaft is reinforced on the outside during the formation of the thread to avoid any risk of tearing the sheet metal. In order to do this the shaft can, for example, be encircled by a rigid ring, optionally constructed by several sections which bear on the outside of the shaft in such a way as to hold it during formation of the thread.

[0008] In addition, before piercing the wall of the cask which initializes the formation of the shaft, a prestamping is advantageously carried out leading to the creation of a preforming dome. The peripheral part of this dome remains at the base of the shaft, which creates a sort of cuvette encouraging the complete emptying of the cask at the end of use. Optional cleaning of the cask is also greatly facilitated by this arrangement.

[0009] The invention will be better understood in the light of the description which follows, given only by way of example and with reference to the attached drawings in which:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0010] FIGS. 1 to 5 illustrate successive operations for forming a bung in a wall of a metal cask according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0011] The drawings illustrate the main operations for forming a bung for a metal cask in accordance with the principle of the invention. The bung is formed in an outside wall 11 of a cask, which is flat or very slightly domed; the bung can also be created in the cylindrical wall of the cask. A first operation illustrated in FIG. 1 includes creating a slight dome 12, by deforming the sheet metal in the wall 11 from the inside toward the outside at the desired location of the bung. An internal cuvette is thus defined. The second operation illustrated in FIG. 2 includes forming an approximately cylindrical shaft 14 by stamping and thus puncturing the wall of the cask at the location of the bung. Because of this, the shaft is connected to the rest of the wall 11 via the peripheral part of the internal cuvette in a relatively pronounced rounded manner that is of such a nature as to subsequently encourage the complete emptying of the cask.

[0012] A third operation illustrated in FIG. 3 includes folding down the protruding edge of the shaft to form an external rolled edge 16. The tooling equipment needed to carry out the operations illustrated in FIGS. 1 to 3 are standard and have therefore not been represented.

[0013]FIG. 4 illustrates a stage that is more particularly representative of the method of the present invention. This stage takes place after the formation of the rolled edge 16. It includes forming a thread inside the shaft. When thin sheet metal is involved, the threading is carried out without removing any metal by using deformation or roller form threading. FIG. 4 shows a roller form threading head 18 before the threading operation. To eliminate any risk of tearing the metal, the shaft is encircled by a rigid ring 20, constituted by at least two annular sections, during the creation of the screw thread. This ring or any similar structure defines a cylindrical annular stop that is applied against the external face of the shaft 14. The sections of the ring define an external tapered bearing surface 22. An external annular monobloc support has a complementary tapered bearing surface (not represented) that bears against the tapered bearing surface 22 in order to keep the sections in place during the threading operation.

[0014]FIG. 5 illustrates the withdrawal of the sections constituting the rigid ring 20 after a thread 26 is formed in the wall of the shaft 14.

[0015] The method has been tested with success on casks made of sheet metal less than 1 mm thick, typically 0.7 to 0.8 mm, for the production of bungs of different sizes ranging from 25 to 60 mm. 

What is claimed is:
 1. Process for the production of a bung for a metal cask consisting in particular of forming an approximately cylindrical shaft (14) by stamping the wall (11) of the cask, characterised in that it consists of forming a thread (26) inside this shaft.
 2. Process according to claim 1, characterised in that it consists of forming the said thread without removing any metal by using roller threading (18) known per se.
 3. Process according to claim 2, characterised in that it consists of reinforcing the outside of the said shaft during the production of the said thread.
 4. Process according to claim 3, characterised in that it consists of encircling the said shaft with a rigid ring (20) or a similar structure during production of the said thread.
 5. Process according to one of the previous claims, characterised in that it consists of folding down the edge of the said shaft to form an external rolled edge (16).
 6. Process according to claim 5, characterised in that the said rolled edge (16) is produced before the said threading (26).
 7. Process according to one of the previous claims, characterised in that it consists of creating a dome (12) in the wall of the said cask at the location of the bung, before formation of the said shaft, in order to obtain an internal cuvette encouraging the complete emptying of said cask. 